LayoutInflater

Want something more than text when you pop up a dialog from your Android app? How about a company logo inside your about box? It’s not hard at all. In this post, I show how to create a menu option for an about box and how to launch a dialog with a custom view when its selected.

First of all, we create an xml layout file for our about dialog and call it about.xml:

This layout contains a RelativeLayout root which means we can a bit more precise with how elements are positioned compared to the LinearLayout where items are stacked side by side either horizontally or vertically depending on the chosen android:orientation setting. Having said that, I’m not doing anything special by using the RelativeLayout here. In fact, I could have achieved the same layout with the LinearLayout but I try to use RelativeLayout where possible as I believe it’s more efficient when rendering, especially when nesting layouts. In this file we have an ImageView that will display the company logo and a TextView that will display the copyright blurb. The actual text and image displayed are resources in the application designated by android:src=”@drawable/icon” and android:text=”@string/about_content” respectively.

Next up, we need a menu that will appear when the Menu button of an Android phone is tapped. Again the content of a menu is determined by an xml file that lives in the res/menu folder named menu.xml:

Having defined our layouts and menus let’s turn to the code. In our Activity we override the onCreateOptionsMenu. When invoked the MenuInflater creates the UI element to display our “About…” menu option using the identifier R.menu.menu, which corresponds to menu.xml

The switch statement only shows the one option (I removed others for clarity) but we could easliy have more which is why we need to know which one was selected hence the call to getItemId() on the MenuItem object which is passed to us by the runtime. Once we determine that the About option was selected we need to turn our xml file, which we declared at the beginning, into a full fledged view instance. This is the job of the LayoutInflater which we grab using the getSystemService method call. Next, the inflate method is invoked passing the id of the layout file that we want to instantiate. This id is automatically generated for us based on the name of the file – about.xml. The second parameter corresponds to the id we gave to the RelativeLayout element in the same file. The end result is a View object which we can pass to the AlertDialog.Builder through the setView method. Finally, when we call show() the dialog is displayed with our image:

Summary

Displaying a dialog with an image essentially comes down to creating a layout file, using LayoutInflater to create an instance, and attaching that instance to the AlertDialog. With a custom layout file your dialog can be as rich as you want.